Plainfield town officials expect to present a bond proposal to residents this fall for multi-million dollar sewer plant upgrade.

The bonding would pay to replace several internal components at the town’s two 45-year-old wastewater treatment stations, a project First Selectman Paul Sweet said will keep the town compliant with more stringent state and federal environmental laws.

“These two plants have only had minor modifications since they were built,” he said. “The plan is to present between a $5.5 million and $6 million bond, to be paid over the course of 20 years. That would work out to about $13 more a year on residents’ tax bills.”

The treatment plants — in the Sunny Brook Village and Central Village sections of town — serve approximately 5,400 users, including some from Sterling. Sweet said town meets all state and federal guidelines for wastewater treatment now, but he expects stricter rules to be instituted soon.

Jeff Young, supervisor for the Water Pollution Control Authority, said the planned upgrades are expected to save the town money in several ways.

“The new systems will be more energy efficient, the settings will be more precise so less energy is expended,” he said. “Also, we’re spending a lot of money for replacement parts — or having to manufacture our own. And that can get expensive.”

The authority’s annual budget for energy costs is roughly $160,000.

Young said there’s also safety concerns to consider when the existing facility has problems.

“In order to make some of these repairs, crews are forced to enter confined spaces 30 feet underground,” Young said. “It’s dangerous.”

The planned upgrades would be limited to the plants’ “guts,” said Lou Soja, the town’s planning and engineering supervisor.

“It’s the pumps, the aerators, the light and motors,” he said. “It would probably take two years to complete the work for the Village plant and then the same for the one in Central Village.”

Since the plants have dual back-ups, no interruption to service is expected.

Sweet said the engineering firm of Fuss & O’Neill is working on project proposals and will host an information forum for residents during an October public hearing. A town meeting and referendum on the bonding will follow, likely by November, Sweet said.

“Anyone can flush a toilet,” he said. “It’s after that that the professionals step up.”